Synesthesia is a phenomenon in which stimulation of one sense triggers an experience in another sense. For example, a voice may be not only heard, but also seen, tasted, or felt as a touch. Common forms of synesthesia include an experience of color or texture triggered by letters, numbers, weekdays, months and musical pitches. While synesthesia has traditionally been studied with small sample sizes (between 1 – 16 subjects), a large scale understanding of this condition has remained elusive. We here present data from over 6,000 rigorously verified synesthetes, whose perceptions have been tested and quantified using our Synesthesia Battery (www.synesthete.org; Eagleman et al, 2007). In addition, while synesthesia has been explored with behavioral and neuroimaging experiments, its genetic basis remains unknown. We present results from our ongoing family linkage analysis, which aims to pull the gene(s) for colored-sequence synesthesia. Synesthesia lends itself well to genetic analysis for 3 reasons: (1) synesthesia runs in family trees, (2) our battery of tests allows confident phenotyping, and (3) synesthesia seems to result from increased cross-talk between neural areas, which suggests a set of candidate genes. For the first time, a rich understanding of the phenomenon of synesthesia - from the genetics to the neuroimaging to the behavior - appears possible, and this understanding will serve as an inroad to the normal operations of neural cross-talk and perception.